What if nature didn’t kill so many caterpillars?
In general, 400 eggs can be laid by one adult butterfly or moth. Out of those 400 butterfly eggs, only about 8 live to become adult butterflies. Nature kills about 98% before they become adults. All three pre-adult stages suffer great losses as they are laid, hatch, grow, pupate, and mature in chrysalis/pupa. These deaths are caused by predators, disease, herbicides, weather, parasitoids, insecticides, and more.
As upsetting as this low survival rate is to many butterfly gardeners and enthusiasts, it is actually necessary in nature. In spite of the fact that nature has a reason for killing so many before they lay eggs, we do our best to help butterflies fight these terrible odds and work to increase butterfly populations.
Why must nature be so deadly? If every egg lived to become adult butterflies and half of the eggs were female, what would happen if all laid an average of 400 eggs and all survived to become adults?
Pretend that there were 6 butterflies of your favorite species flying in your yard, 3 were male and 3 were female, let’s go with the total survival scenario. Assume that the 3 females each laid 400 eggs and all 400 eggs survived and become adult butterflies. Continue supposing that half were female and half were male. Finally, let’s suppose each butterfly continued the cycle of life generation after generation.
I’m in north Florida where most species can go through 8 or so generations per year. But let’s do numbers for areas where butterflies can go through only 3 generations per year.
Are you ready for the reason why nature’s habit of killing so many eggs, caterpillars, and chrysalises is a good thing?
400 eggs each x 3 female butterflies = 1,200 butterflies (assume they are half male, half female).
400 eggs each x 600 female butterflies = 240,000 butterflies (assume they are half male, half female).
400 eggs each x 120,000 female butterflies = 48,000,000 butterflies (assume they are half male, half female).
It is already beyond the realm of possibility. Why?
First, host plants are essential for caterpillars. They are the plants that caterpillars MUST eat to survive. This huge number of caterpillars would decimate all the particular host plants for most species within one to two generations. It would not take long for that species of butterflies to become extinct. Caterpillars would starve because the host plants had been eaten and they could not become adult butterflies.
As we think of the most popular butterfly, the Monarch, can you imagine how much milkweed 48,000,000 caterpillars would eat?
Some species would continue for more generations than others but no species could not go many generations at those exponential rates. Duskywing butterflies that eat oak tree leaves, Viceroys that eat willow leaves, Red-Spotted Purples that eat willow and black cherry (and a few other plants), and others who eat plants that are large and cover much of the area would have more leaves. But they would not have enough leaves (caterpillar food) to continue reproducing at such an explosive rate.
Remember, we are talking about only ONE species starting with THREE female butterflies. Estimates of the number of species of butterflies in the world range from 15,000 to 30,000. Multiply the number above by the number of species in the world … (did you multiply?) … quite unimaginable, isn’t it?
Let’s go for three more generations:
400 eggs each x 24,000,000 female butterflies = 9,600,000,000 butterflies (half male, half female).
400 eggs each x 4,800,000,000 female butterflies = 1,920,000,000,000 butterflies (half male, half female).
400 eggs each x 960,000,000,000 female butterflies = 384,000,000,000,000 butterflies ….
That reads three hundred eighty four TRILLION butterflies within six generations, generated from three female butterflies of just one species.
Then I sit and wonder about this. What if it were possible for all of them to live? I wonder how long it would take before we would lose the ability to drive due to butterflies on windshields and clogging up radiators …